Organic photoconductors, used in electrophotographic apparatuses such as copying machines or printers employing electrophotographic techniques, conventionally comprise a conductive substrate and an organic photoconductive layer laminated on the conductive substrate. The photoconductive layer is made of organic materials including an organic photoconductive material. The conductive substrate is usually cylindrical due to design specifications of the electrophotographic apparatuses. The photoconductive layer, a thin film that contains an organic photoconductive material, is formed on the outer surface of the cylindrical substrate.
Aluminum or aluminum alloys which are light in weight and which have excellent machinability have been widely used as substrate materials. However, it is necessary to machine with high precision the outer surface of each cylindrical aluminum or aluminum alloy substrate to meet the dimensional specifications (circularity: .+-.50 .mu.m or less, diameter: .+-.40 .mu.m or less) and to realize the preferred surface roughness (0.5 to 1.2 .mu.m for the maximum height R.sub.MAX). It is also necessary to insert a flange for precise rotation in forming a photoconductor layer by layer. And since the surface of an aluminum or aluminum alloy substrate is susceptible to oxidation or transformation by atmospheric oxygen or moisture, countermeasures are necessary such as providing the substrate surface with a protective anodized oxide film. Thus, aluminum or aluminum alloy substrates have been manufactured through many manufacturing steps and at high manufacturing cost.
Japanese Patent Document No. H02-17026 discloses a cylindrical substrate that is lighter in weight, chemically and thermally highly resistant, neither oxidized nor deformed in air, and suitable for organic photoconductors. The cylindrical substrate is manufactured by injection molding of materials including a polyphenylene sulfide resin (hereinafter referred to as "PPS resin").
With a volume resistivity of pure PPS resin of 10.sup.14 to 10.sup.16 .OMEGA..multidot.cm, electrical conductivity of such a substrate is too low for the photoconductor to be viable in electrophotography. For obtaining images or prints clear enough for practical use, the volume resistivity of the substrate should be less than 10.sup.4 .OMEGA..multidot.cm. A volume resistivity exceeding 10.sup.5 .OMEGA..multidot.cm hinders the electric charges from transferring to the substrate during light exposure or discharge and raises the remanent potential. Thus, the high volume resistivity of PPS resin makes it unsuitable for obtaining clear images or prints. Carbon black is added, for example, to provide the PPS resin with enhanced electrical conductivity. Since the volume resistivity of carbon black such as conductive furnace carbon is 10.sup.-1 to 10 .OMEGA..multidot.cm, it is necessary to add as much as 15 weight % carbon black to the PPS resin to reduce the volume resistivity of the substrate to 10.sup.4 .OMEGA..multidot.cm. However, the addition of carbon black has its limits, as large amounts of carbon black addition reduce the mechanical strength of the substrate. Moreover, it is difficult to attain the required dimensional substrate precision if the substrate is made of normal linear PPS resin which, as compared with crosslinked PPS, is deformed more easily by the solvent of a coating liquid or by heating.
Though the PPS resin substrate has excellent chemical resistivity as described above, the adhesiveness of the PPS resin substrate to the organic photoconductive layer formed thereon is low, which may result in peeling of the coated and dried photoconductive layer from the substrate. Moreover, peeling of the photoconductive layer from the substrate can be caused in practical use by repeated contact with other parts and components of the electrophotographic apparatus. Thus, the production efficiency of the PPS resin substrate is low and its product life is short.